Mechanical combination locks such as those found on safes, vaults, cabinets and other high security enclosures are well known and subject to a number of attacks, such as by drilling, manipulation, and computer controlled auto dialing.
Electronic combination locks for such enclosures have been invented which provided the opportunity to increase the level of security afforded by the lock, while at the same time overcoming many of the shortcomings of the prior art mechanical locks. Two examples of these locks may be found at. U.S. Pat. No. 5,061,923 entitled Computerized Combination Lock and U.S. Pat. No. 5,517,184 entitled Electronic Combination Lock with High Security Features.
Recently an improved high security electronic combination lock has been invented which provides the opportunity to greatly increase the level of security afforded by the lock, while at the same time overcomes many of the short comings of prior art mechanical and electronic locks.
A dial type mechanical combination lock relies on the rotation of a knob to positions represented by numbers on the dial to rotate mechanical elements within the lock, such that the wheels of the mechanism align to allow a bar to drop into the wheels and retract the lock bar or bolt, allowing the enclosure to be opened.
The electronic combination lock does not have the equivalent mechanical elements and, therefore, cannot be attacked in the same manner. For example, the mechanical lock may be drilled to permit the insertion of an optical device into the lock mechanism to observe the positions of the wheels and thus their alignment, which permits the opening of the enclosure without the knowledge of the combination.
The electronic lock cannot be drilled for a similar purpose since the electronic lock mechanism will not reveal the position of any element, which gives the attacker any information as to the combination needed to unlock the device. The mechanical lock has a fixed position of internal elements relative to the dial and thus may be observed with the movements of the dial repeated by the attacker, at a later time. The electronic lock may not have a fixed knob to number position relation and thus observation of the movement of the knob is much more difficult if not impossible.
Dialers exist which may be attached to the knob on a mechanical or electrical combination lock and which dial combinations under the control of a computer. As each combination fails, the computer then continues to dial other combinations to eventually unlock the lock. With a combination lock of the mechanical type and sufficient time, a dialer is particularly effective.
Therefore an electronic combination lock is needed that limits the effectiveness of observation of knob position by employing a random time delay from the time the knob starts turning to enter a combination until the display is activated and begins incrementing the number displayed. Additionally, an electronic combination lock is needed that will, from a practical standpoint, prevent the use of an auto dialer or a person from determining the correct combination.
The electronic combination lock disclosed and described herein solves the problems discussed above and is a combination lock having a knob, which requires no divisions or markings relating to the numbers of the combination thereon. The rotation of the knob drives a generator, which produces electrical power. The power generated serves as a power source for the electronics of the lock. A knob rotation detector provides a signal to the microprocessor. The microprocessor utilizes this signal to determine the speed and amount of rotation of the knob.
The program controls the microprocessor. The ability to control the microprocessor with a microcode control program is an advantage in that the many functions and features may be added to make the lock mechanism and the enclosure more secure.
When the knob is rotated, the knob position detector sends a signal to the microprocessor. This signal is received by the microprocessor. The signal enables the microprocessor to determine the speed of rotation of the knob. As the speed of the rotation of the knob varies, the rate of change of the displayed numbers may change. This is accomplished so that at a high rate of knob rotation the displayed numbers may change at a high rate while at the lower rates or rotation, the rate of change of the displayed numbers may be at a slower rate. Further, the number of degrees the knob must be turned to effect the change of the displayed number will vary so that there may be no consistent amount of rotation required to change the displayed number by one unit. This aspect of the lock also acts to foil the use of a computer-controlled dialer.
The timing capabilities of the lock provide the opportunity to set the minimum time that can be used in the entering of the combination. The lock waits a period of time, typically, two seconds between the entry of one element of the combination and the lock permitting the entry at the next element of the combination. This wait time forces a large amount of time to be expended in trying each combination in an effort to open the lock. With a two-second wait between each combination element (0-99) and using a three-element combination it would take a minimum of 1,667 hours to enter the one million possible combinations.
The microprocessor may also count the failed attempts to open the lock since the last successful operation. If the numbers of tries or attempts to unlock the lock equals or exceeds the number set in the microprocessor microcode, the lock will fail to open even if an authorized combination is subsequently entered. After an error indication is displayed, the lock may be disabled to prevent further entry tries.
In order to eliminate the possibility of correlation between the number displayed and/or entered and knob position, there may be a random time delay between the start of knob rotation and the incrementing the number displayed.
When a condition is created where the lock will not open even with the eventual entry of the authorized combination, the lock electronics must be reset. The reset is accomplished by entering a reset combination or code.